Dawn was breaking over the Norfolk farmlands when Eddie Brigham steered his tractor into the path of an oncoming mower that had been let loose to damage his six-acre crop of maize.

To the disappointment of 28 Greenpeace activists, the collision crumpled the mower, but the events at Walnut Tree Farm left an indelible mark on the history of anti-GM crop campaigning. The year was 1999 and the raid targeted one of the most controversial experiments Britain has seen: field-scale trials of GM crops.

Eight years on, the government is paving the way for GM crops to be planted once again. Ministers believe that the case has been strengthened by the global food shortage and the need to grow crops for biofuels to combat climate change.

Strong opposition to GM emerged in Britain in the early 1990s as crop varieties created by multinationals such as Monsanto began to clear regulatory hurdles.

Pressure groups seized on the issue and English Nature was worried that herbicides to be used with GM crops would be so effective that they would leave no weeds or seeds for bugs or butterflies on the farmland margins. If they took a hit the knock-on effects further up the food chain could be devastating, they feared.

In 1997 it became clear that GM soya from Monsanto had reached British supermarkets unlabelled, in processed food. A year later the Prince of Wales suggested consumers boycot GM entirely.

In the face of growing opposition, Michael Meacher, then environment minister, negotiated a voluntary moratorium with the GM industry, which agreed not to plant crops until broad farm-scale trials had been carried out to assess the ecological impact. Europe imposed its own moratorium, banning the import or growing of GM crops. In spring 1999 the first GM trial began in Wiltshire.

Before the trials were complete the government commissioned two reviews. Sir David King, the chief science adviser, gathered 24 scientists to sift through scientific literature, looking for dangers. The Cabinet Office, meanwhile, conducted a costs and benefits assessment.

In July 2003 the science review concluded that weedkillers posed a potential threat to wildlife and that if GM crops were planted widely throughout Britain traditional and organic farms could become contaminated because GM pollen would carry on the wind. The Cabinet Office report concluded that any benefits for consumers would be minimal.

The government launched a public debate on GM, involving 675 public meetings and nearly 40,000 written responses. The consultation was dominated by groups firmly for or against GM, and found that 86% were unhappy to eat GM and 91% feared for its effects on the environment.

When results from the farm-scale trials were published later in the year they revealed that the powerful weedkillers used with some GM crops led to drops in farmland bees and butterflies.

In 2004 the government approved GM maize for planting, but by this time many biotech companies had scaled down their plans in Britain or pulled out entirely.

But it now appears that the industry was biding its time in the hope that anti-GM sentiment would die down. Last year the German company BASF gained permission for the first GM crop trial in Britain since the government's own. Its blight-resistant potato will be planted at two fields as part of a five-year evaluation.

Timeline

1983 Scientists genetically modify a plant, creating tobacco that is resistant to an antibiotic.

1992 The phrase "Frankenfood" is coined by Paul Lewis, an English professor at Boston College.

1994 The first GM food, the Flavr Savr tomato, is approved in the US.

1996 GM tomato paste arrives on British supermarket shelves.

1999 The field scale trials of GM crops begin across Britain.

2003 Farm scale trials conclude that herbicides used with some GM crops can reduce weeds and seeds for farmland wildlife.